Bono has been forced to abandon the stage during a U2 concert in Berlin after losing his voice several songs in. The 58-year-old had struggled from the start of the Saturday night show and repeatedly sipped a hot drink. After performing Beautiful Day with the help of fans who he encouraged to sing along, the US frontman took a break backstage - and didn't return. Fans at Berlin's Mercedes-Benz Arena were then informed that the concert would not continue. No reasons were given. Ticket-holders are to receive tickets for another U2 concert on an as yet unspecified date. At the start of U2's current European tour on Friday, Bono had criticised recent right-wing unrest in the eastern German city of Chemnitz. During that show on Friday night, a video display suddenly flashed the hashtag #wirsindmehr in German, to cheers from concertgoers. The slogan "wir sind mehr" (We are more) has become a hashtag rallying cry against right-wingers in Chemnitz. Australian Associated Press